This Small Business Technology Transfer Phase I project will undertake innovative heat transfer research involving dropwise condensation on a wettability gradient. Dropwise condensation alone has shown the ability to increase condensation heat transfer coefficients by an order of magnitude over film condensation, typical of vertical thermosyphons. Droplets condensing on a gradient surface experience different contact angles, causing the droplets to accelerate to high velocities in the direction of increased wettability. The difference in contact angle on opposite sides of the condensing droplets is due to locally varying properties of the condensing surface, controlled by varying surface concentrations of molecules with low surface energy. The higher droplet velocities caused by condensing on the gradient surface further increases the heat transfer coefficient over typical dropwise condensation. Furthermore, the gradient surface does not require gravity to remove liquid from the condensing surface enabling dropwise condensation heat transfer coefficient values on horizontal surfaces and in microgravity applications. The broader impact/commercial potential from this project is that the technology will have the ability to impact heat transfer solutions in various commercial applications where the ability to dissipate more power is parallel to better performance. In the computer processing industry, solutions for notebook computers and servers are becoming increasingly limited by the thermal solution. In micro-gravity environments a gradient surface will replace or enhance the capillary forces currently used in heat pipe devices,
such as axially grooved heat pipes and loop heats for spacecraft applications. There is already a demand for higher capacity thermal solutions, and this demand will only increase as commercial companies and government agencies expand their capabilities and demand greater thermal dissipation. This research will further the fundamental understanding of liquid movements due to surface gradients and similar Marangoni flows. Uses of similar Marangoni flows, such as temperature gradient induced flows, are currently the focus of many studies regarding fluid pumping in microfluidic applications.